1. Field of the Invention
The invention pertains to the art of image processing and, more particularly, to image reduction.
2. Description of Related Art
The following description includes references to slow-scan and fast-scan digital image data when discussing the orientation of selected window coordinates and sampled image data signals used by control circuitry. For purposes of clarification, data collected along a fast scan direction is intended to refer to individual pixels located in succession along a raster of image information. On the other hand, data collected in the slow-scan direction refers to data derived from a common raster position across multiple rasters of image information. As an example, fast-scan data would refer to the sequential signals collected along the length of the linear photosensitive array during a single exposure period, and is commonly referred to as a raster of data. Slow-scan data would be used to describe signals captured from a plurality of elements along a linear photosensitive array, as the array was moved relative to a document. Analogously, your eyes move in the fast-scan direction relative to this page as you read along each line; when your eyes move to the next line down, they have moved in the slow-scan direction.
Various digital image processing techniques are known for manipulating static images which are later output onto such media as the screen of a personal computer or onto printed paper. One of these processes is reducing the size of an image. Van Nostrand, in U.S. Pat. No. 5,008,752, discloses a method to reduce an image by providing interpolated data in two dimensions. The process includes row and column interpolators operating to generate signals indicating when the next element, row or pixel is to be retrieved. The interpolators also produce a displacement address, which is used to retrieve an interpolation coefficient from a look-up table, the interpolation coefficient being used subsequently to produce the interpolated output. Unfortunately, the look-up tables require extensive use of costly memory devices.
Another method is disclosed by Calarco et al. in U.S. Pat. No. 5,237,432 to obtain two successive input pixel values, Pn and Pn+1. At the same general time, an arithmetic accumulation of the sum of a seed value, a previously accumulated sum, and a supplemental value is calculated. Typically, this accumulated sum has both integer and fractional portions. Once determined, the integer portion of the accumulated sum is used to determine whether the first and second input pixel values are to be used to produce an output pixel value. If so, the accumulated sum is used to generate a scale or interpolation factor, xcex1, based upon the fractional portion of the accumulated sum, which, in turn is used to interpolate between the first and the second pixel values to produce an output pixel value where: Pnew=Pn+1+xcex1(Pnxe2x88x92Pn+1). The process is continued until all input pixels have been processed.
However, the integer portion of this process eliminates pixels according to a sequence that corresponds to the desired scaling. For example, if an image is to be reduced by 50%, every other pixel is discarded, if the desired reduction is 33%, every third pixel is discarded. In fact, regardless of the scale factor desired, an output pixel created from the linear interpolation technique of Calarco et al., will only take into account the four nearest neighbor pixels. Thus, the output image can have uneven shading and other image degradations.
The present invention contemplates a new, efficient reduction technique, which overcomes the above-referenced problems and others and provides a more accurate implementation of pixel window averaging.
In accordance with the present invention, there is provided an image processing system for reducing an image by a desired scaling factor. The image comprises a plurality of video signals each having a magnitude, so that the system can represent the image with a number of output video signals. The system includes averaging means for determining an average magnitude associated with a defined set of input video signals where the set is defined by the scaling factor. Video signal output means are also provided for outputting the output video signal comprising the average magnitude.
In accordance with another aspect of the present invention, the scaling factor includes a fast scan component which is inversely proportional to a fast-scan seed factor and a slow scan component which is inversely proportional to a slow-scan seed factor.
In accordance with another aspect of the present invention, the defined set of input video signals includes a number of whole and partial input video signals in both the slow scan direction and in the fast scan direction.
In accordance with another aspect of the present invention, the averaging means is an electrical circuit including an adder for summing a plurality of the video signal magnitudes. The adder also provides a partial sum of the magnitudes which is temporarily stored in a memory device.
In accordance with another aspect of the present invention, a multiplier is provided for producing the average magnitude by determining the product of a total sum of the magnitudes in the set multiplied by the inverse of a product of the fast scan seed factor and the slow scan seed factor.
In accordance with another aspect of the present invention, a number of memory locations are determined for the memory device by comparing a leading edge of the input video image with the fast scan seed factor.
In accordance with another aspect of the present invention, the output video signal having the average magnitude of the set is output in real time.
In accordance with another embodiment of the present invention, a method is disclosed for reducing an image in accordance with a scaling factor. The scaling factor is received defining a set of input video signals. The magnitudes of the set of are summed together and averaged. An output video signal having the average magnitude is output for each set.
In accordance with another aspect of the present invention, for a number of slow scan lines corresponding to a seed factor in a slow scan axis, the summing includes summing the magnitude of a number of fast scan input signals corresponding to a seed factor in a fast scan axis.
The result from the summing step is temporarily stored until a total magnitude of the input video signals within a set is summed.
In accordance with another embodiment of the present invention, an imaging device capable of scanning an image thus producing a stream of input video signals eligible for reduction in accordance with a scaling factor is provided. The imaging device includes means for determining an average magnitude of a set of the input video signals where the set is determined by the scaling factor.
One benefit obtained by use of the present invention is that the reduced output image will more faithfully represent the input image.
Another benefit obtained from the present invention is real-time processing.
Yet another benefit obtained from the present invention is reduced memory requirements.
Other benefits and advantages of the subject new method and apparatus will become apparent to those skilled in the art upon a reading and understanding of this specification.